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Re: Character Array vs String

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On 11/21/2011 2:39 AM, David Thompson wrote:
[...]
> But to answer the exact question, DEC PDP-10 computers had a 36-bit
> word with (few) special 'byte' instructions that could access *any*
> number of bits within a word (and historically on a range of machines
> bytes are not always 8 bits). Most software on 10's either divided
> each word into 6 characters of 6-bits using the printable uppercase
> subset of ASCII (i.e. columns 2 to 5), or into 5 characters of 7-bit
> ASCII with 1 bit left over. (In those days nearly all terminals and
> printers were uppercase-only anyway.) Some software did use 8-bit
> bytes with 4 bits left, or 'spanned' 9 bytes of 8-bits over 2 words,
> or had 4 bytes of 9-bits per word. I suppose some software may even
> have done 7 bytes of 5-bits leaving 1 using Baudot/ITA2 or similar.
[...]

While there were a few PDP-n's on campus as I recall, the main computer lab 
at the college I went to used a KL-10.  While I hadn't heard of C way back 
when, I did some assembly programming on it.

As you say, it had 36-bit words, and 18-bit addresses.  The O/S used six 
6-bit characters per word for filename, which IIRC were in 6.3 format.  (I 
guess they used the other 18 bits for file attributes?)  Text was typically 
stored as five 7-bit characters, with 1 bit padding.

Yet, although addresses were 18 bits wide, and each address pointed to a 
36-bit word, a "pointer" count, in fact, be wider than 18 bits.  For 
example, there were machine instructions for accessing sub-words, including 
things like "take the 7 bits at this address/bit-location, move it to the 
low-order 7 bits at this address, zero-padding it, and then increment the 
pointer by 7 bits".  (Of course, C requires at least 8 bits per char, so I 
guess it would use the same thing, but storing four 8-bit chars per word 
with 4 padding bits.  You could store four 9-bit chars w/o any padding, but 
files on disk were 8-bit characters, so it probably wouldn't make sense to 
do so.)

As I said, I never saw a C compiler for it, but I would suspect that 
sizeof() would be "interesting" on such a system.  The simplest system would 
be to simply store one 8-bit char per 36-bit word, but that seems rather 
inefficient.

-- 
Kenneth Brody

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Character Array vs String Sheky <shekhar07.nitdgp@gmail.com> - 2011-11-09 03:09 -0800
  Re: Character Array vs String Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-09 03:28 -0800
  Re: Character Array vs String James Kuyper <jameskuyper@verizon.net> - 2011-11-09 06:52 -0500
  Re: Character Array vs String Quentin Carbonneaux <qcarbonn@invalid.com> - 2011-11-09 12:01 +0000
    Re: Character Array vs String 88888 Dihedral <dihedral88888@googlemail.com> - 2011-11-09 04:48 -0800
      Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-09 05:53 -0800
        Re: Character Array vs String "osmium" <r124c4u102@comcast.net> - 2011-11-09 09:44 -0600
          Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-10 00:57 -0800
            Re: Character Array vs String "osmium" <r124c4u102@comcast.net> - 2011-11-10 08:56 -0600
              Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-10 08:16 -0800
                Re: Character Array vs String "Joachim Schmitz" <nospam.jojo@schmitz-digital.de> - 2011-11-10 18:34 +0100
                Re: Character Array vs String Kenneth Brody <kenbrody@spamcop.net> - 2011-11-10 14:08 -0500
                Re: Character Array vs String Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-10 20:52 +0000
                Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-11 01:29 -0800
              Re: Character Array vs String Lowell Gilbert <lgusenet@be-well.ilk.org> - 2011-11-10 12:29 -0500
              Re: Character Array vs String lawrence.jones@siemens.com - 2011-11-10 12:32 -0500
                Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-10 12:41 -0800
                Re: Character Array vs String jt@toerring.de (Jens Thoms Toerring) - 2011-11-11 13:12 +0000
              Re: Character Array vs String David Thompson <dave.thompson2@verizon.net> - 2011-11-21 02:39 -0500
                Re: Character Array vs String Kenneth Brody <kenbrody@spamcop.net> - 2011-11-23 11:39 -0500
                Re: Character Array vs String "BartC" <bc@freeuk.com> - 2011-11-23 17:15 +0000
                Re: Character Array vs String Kaz Kylheku <kaz@kylheku.com> - 2011-11-23 18:48 +0000
                Re: Character Array vs String Ben Pfaff <blp@cs.stanford.edu> - 2011-11-23 10:58 -0800
                Re: Character Array vs String Patrick Scheible <kkt@zipcon.net> - 2011-11-27 20:21 -0800
                Re: Character Array vs String David Thompson <dave.thompson2@verizon.net> - 2012-01-19 02:43 -0500
        Re: Character Array vs String Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-09 07:48 -0800
          Re: Character Array vs String James Kuyper <jameskuyper@verizon.net> - 2011-11-09 11:06 -0500
            Re: Character Array vs String Willem <willem@toad.stack.nl> - 2011-11-09 16:24 +0000
              Re: Character Array vs String James Kuyper <jameskuyper@verizon.net> - 2011-11-09 11:30 -0500
                Re: Character Array vs String "BartC" <bc@freeuk.com> - 2011-11-09 16:53 +0000
                Re: Character Array vs String Willem <willem@toad.stack.nl> - 2011-11-09 17:05 +0000
                Re: Character Array vs String Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-09 08:54 -0800
                Re: Character Array vs String Tobias Blass <tobiasblass@gmx.net> - 2011-11-09 21:01 +0000
                Re: Character Array vs String "BartC" <bc@freeuk.com> - 2011-11-09 21:26 +0000
                Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-10 01:11 -0800
                Re: Character Array vs String David Thompson <dave.thompson2@verizon.net> - 2011-11-21 02:39 -0500
                Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-21 00:15 -0800
                Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-09 14:06 -0800
                Re: Character Array vs String Stephen Sprunk <stephen@sprunk.org> - 2011-11-09 19:32 -0600
                Re: Character Array vs String Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-10 03:21 +0000
                Re: Character Array vs String "BartC" <bc@freeuk.com> - 2011-11-10 11:00 +0000
                Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-10 03:26 -0800
                Re: Character Array vs String Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-10 12:04 +0000
                Re: Character Array vs String Lew Pitcher <lpitcher@teksavvy.com> - 2011-11-21 12:02 -0800
                Re: Character Array vs String Kenneth Brody <kenbrody@spamcop.net> - 2011-11-23 11:42 -0500
                Re: Character Array vs String Uno <merrilljensen@q.com> - 2011-11-27 22:46 -0700
                Re: Character Array vs String Lew Pitcher <lpitcher@teksavvy.com> - 2011-11-27 23:30 -0800
                Re: Character Array vs String Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-28 00:22 -0800
        Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-09 13:59 -0800
    Re: Character Array vs String James Kuyper <jameskuyper@verizon.net> - 2011-11-09 08:36 -0500
      Re: Character Array vs String Quentin Carbonneaux <qcarbonn@invalid.com> - 2011-11-09 14:06 +0000
    Re: Character Array vs String Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-09 05:38 -0800
    Re: Character Array vs String Keith Thompson <kst-u@mib.org> - 2011-11-09 13:52 -0800
  Re: Character Array vs String Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-09 07:39 -0500
  Re: Character Array vs String "BartC" <bc@freeuk.com> - 2011-11-09 13:51 +0000
  Re: Character Array vs String John Bode <jfbode1029@gmail.com> - 2011-11-23 19:32 -0800
    Re: Character Array vs String James Kuyper <jameskuyper@verizon.net> - 2011-11-24 11:49 -0500

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